This invention relates to an improved system for detecting the existence of emergency conditions, such as an undesirable shifting of attempted theft of products from truck beds, warehouses or the like, or the occurence of a fire hazard.
There is a need for a simple and inexpensive detection system which will create a warning signal when an emergency condition exists, and which can be readily reactivated for further use after the emergency condition has passed. For instance, the customary shipment of products in open or accessible truck beds has created a substantial pilferage and theft problem. Even the largest equipment on a truck bed is subject to theft if the truck includes no detection system. Truck operators are also constantly subjected to the danger of shifting loads during transit. In addition, there are many installations requiring a simple and fail-safe system for detecting the existence of an undesirable heat build-up which would create a fire hazard. There is also a need to provide a monition and fire detection system that is essentially non-electrical, so that no substantial electrical power supply is needed to maintain the detection system in operation.
Accordingly, the principle object of this invention is to provide a simple, economical and reliable detection system which will meet the above needs. Generally, the system comprises a pressure line which is extended throughout the material or the area to be guarded. The line is charged with a suitable pressurized fluid, such as nitrogen or compressed air to establish a selected line pressure. Break unions of special design are provided at selected locations in the line. In one embodiment, the break unions are designed to disconnect from the line upon the application of a predetermined force to the line to thereby reduce the line pressure and activate an alarm incorporated within the system. In a second embodiment the break unions are designed to be fusible links which break the line and thereby reduce the line pressure by melting at a selected temperature level. In accordance with this invention the unions are readily replaceable, so that the line can be recharged, and the alarm system reactivated, after the emergency condition has passed.
More specifically, the alarm system in accordance with this invention includes an elongate pressure line constructed from a flexible material such as polyethelyne. The line has a central opening which is sealed in a fluid-tight condition, and is charged with a pressurized fluid to establish a selected line pressure. A pressure-responsive switch is included in the system and is maintained in an inactive position under normal conditions. When an emergency condition occurs and the line pressure is reduced, the switch responds to the pressure change by moving into an alarm position and thereby activates a suitable visual or audible alarm. A plurality of break unions, including a bore which maintains the fluid continuity of the line, are spaced at selected points along the line. Spring-biased retaining means apply a selected clamping force to the line adjacent the unions to seal the unions in the line. The unions respond to the application of a selected force to the line, or to the existence of a predetermined temperature level, to break the seal of the line and thereby activate the alarm incorporated within the system.